1. Field of the Invention
The present invention concerns vaccines effective for treating cancer. This invention particularly concerns a universal cancer vaccine involving telomerase reverse transcriptase as a specific tumor antigen, a method for its use for targeting cytotoxic T lymphocytes to tumor cells, and a method for induction and/or augmentation of a cancer patient's immune response against his tumor.
2. Description of the Prior Art
Various publications are referenced within this application. The disclosures within these publications are hereby incorporated by reference, in their entireties, into this application so that the state of art to which this invention pertains is more fully described.
The prevalent cancer treatments of choice heretofore are surgery, radiation, chemotherapy or a combination thereof. With the exception of a very few cancers, prognosis has not been very satisfactory, resulting in death of the patient after sometimes horrendous suffering from the treatments themselves.
Many medical research laboratories throughout the world are doing research directed towards developing effective, non-invasive treatments for arresting the growth and destroying both benign and malignant tumors. However, treatments employed, both in clinical trials or general practice, have not demonstrated appreciable levels of tumor cell necrosis thus far.
Aspecific Methods of Treatment
One method for treating tumors, brachytherapy, involves injecting microscopic clumps of the protein albumin directly into the tumor. A suitable amount of radioactive phosphorous is then added through the same needle. The albumin clogs capillaries within the tumor, thereby, preventing the release of radioactive phosphorous to tissues outside the tumor. Tumor cells take up and use the phosphorous rapidly, selectively killing them with radioactivity without damaging normal cells in other parts of the body. By the time the capillaries become unclogged, all or most of the radioactive phosphorous has been absorbed by the cells comprising the tumor, leaving little to escape into adjacent tissue. This therapy, however, is difficult to implement and always carries the danger of radioactive material escaping into healthy parts of the body causing serious damage.
Robert T. Gordon in U.S. Pat. No. 4,622,952 disclosed a different method for treating tumors. This method attempts to take advantage of the observed different heat sensitivity between tumor and normal cells. It is well known that tumor cells are killed at lower temperatures than normal cells. Thus, Gordon proposed a method using electromagnetic energy to elevate the temperature of tumor cells or tissues, to kill the tumor cells without seriously affecting normal cells.
Immunotherapy
1. Antibody Response
Many attempts have been made to kill tumor cells with polyclonal or monoclonal isoantibodies or autologous antibodies elicited against tumor-specific antigens. Generally, this method is not successful, especially when dealing with solid tumors.
2. Cytotoxic Immunity
Unfortunately, these approaches for the prevention and/or treatment of cancer have not been successful or completely satisfactory because of a number of problems, such as the absence in the vaccine of tumor antigens expressed by the tumor to be treated, poor characterization of the antigens in tumor vaccines, the contamination of vaccines by immunogenic but undesirable material, such as fetal calf serum (FCS) protein or transplantation antigens and additionally due to the antigenic heterogenicity of the cancer cells. Moreover, such tumor vaccines were often prepared from fresh tumor cells, the supply of which is limited so that the properties of the vaccines are not reproducible.
3. Current Concepts
Selecting an Aspecific Target Substance.
U.S. Pat. No. 5,658,234, issued to Dunlavy in 1997 describes a method for treating a tumor comprising the steps of selecting a target substance which has at least one component with an atomic or molecular resonance frequency or frequencies different from the atomic, molecular or cellular resonant frequencies of normal cells, locating or depositing the target substance within the tumor, and irradiating the target substance with electromagnetic wave energy at a frequency or frequencies corresponding to the atomic or molecular resonance of the component such that the component absorbs energy from the electromagnetic wave, resulting in the release of heat sufficient to destroy, terminate or slow the growth of the tumor without adversely affecting the viability of normal cells.
a. Specific Melanoma Antigens
Melanosomal antigens can be recognized by the immune system. This has been demonstrated by immunoprecipitation of a gp75 antigen from autologous melanoma cells by serum IgG antibodies of a patient with metastatic melanoma (Mattes, J. M., T. M. Thomson, L. J. Old, and K. O. Lloyd. (1983) A pigmentation associated, differentiation antigen of human melanoma defined by a precipitating antibody in human serum, Int. J. Cancer. 32:717). The gp75 antigen is a melanosomal polypeptide that is the most abundant glycoprotein synthesized by pigmented melanocytes and melanomas. (Tai, T., M. Eisinger, S. Ogata, and K. O. Lloyd. (1983) Glycoproteins as differentiation markers in human malignant melanoma and melanocytes, Cancer Res. 43:2773). Epidermal melanocytes, benign pigmented lesions, and primary and metastatic melanomas express gp75, but other cell types do not (Thomson, T. M., F. X. Real, S. Murakami, C. Cardon-Cardo, L. J. Old, and A. N. Houghton. (1988) Differentiation antigens of melanocytes and melanoma: Analysis of melanosome and cell surface markers of human pigmented cells with monoclonal antibodies, J. Invest. Dermatol. 90:459). In the present invention, it is demonstrated that gp75 cDNA had approximately 90% identity with the derived amino acid and nucleotide sequences of a mouse gene that maps to the b (brown) locus. The brown locus is a site that determines coat color and influences the type of melanin synthesized, suggesting that gp75 may regulate or influence the type of melanin synthesized.
The fact that IgG antibodies in sera of a patient with metastatic melanoma have been shown to immunoprecipitate gp75 demonstrates that immunological tolerance against gp75 can be broken. This invention therefore provides expression vectors comprising gp75 cDNA for use as a vaccine against melanoma, whereby the amino acid sequences of peptides were determined from gp75 polypeptide, which was isolated and purified by the mouse monoclonal antibody TA99, and whereby cDNA clones were isolated by screening with oligonucleotides based on the peptide sequences.
b. Human Prostatic Specific Reductase.
U.S. Pat. No. 6,106,829, issued to He, et al. uses a human prostatic specific reductase polypeptide as a diagnostic marker for prostate cancer and as an agent to determine if the prostate cancer has metastasized. The patent also discloses antibodies specific to the prostatic specific reductase polypeptide that may be used to target prostate cancer cells and be used as part of a prostate cancer vaccine.
c. Telomerase
Another method for treating tumors currently being evaluated by medical researchers makes use of a substance called telomerase, an enzyme that tumor cells produce and require to remain alive, but which normal body cells (except for sperm and hematopoietic system) neither produce nor require. This unique property of telomerase has prompted attempts to develop a drug that will block the action of the enzyme sufficiently to either inhibit the growth of new tumor cells or cause the death of older ones. Telomerase is an example of a class of substances that are often referred to as being “tumor-specific” because they are needed and/or used by tumor cells in differentially larger amounts than by normal healthy cells of the body.
Telomeres, the protein-DNA structures physically located on the ends of the eukaryotic organisms, are required for chromosome stability and are involved in chromosomal organization within the nucleus (See e.g., Zakian, Science 270:1601 [1995]; Blackburn and Gall, J. Mol. Biol., 120:33 [1978]; Oka et al., Gene 10:301 [1980]; and Klobutcher et al., Proc. Natl. Acad. Sci., 78:3015 [1981]). Telomeres are believed to be essential in such organisms as yeasts and probably most other eukaryotes, as they allow cells to distinguish intact from broken chromosomes, protect chromosomes from degradation, and act as substrates for novel replication mechanisms. Telomeres are generally replicated in a complex, cell cycle and developmentally regulated, manner by “telomerase,” a telomere-specific DNA polymerase. However, telomerase-independent means for telomere maintenance have been described. In recent years, much attention has been focused on telomeres, as telomere loss has been associated with chromosomal changes such as those that occur in cancer and aging.
Importantly, telomere replication is regulated both by developmental and cell cycle factors. It has been hypothesized that aspects of telomere replication may act as signals in the cell cycle. For example, certain DNA structures of DNA-protein complex formations may act as a checkpoint to indicate that chromosomal replication has been completed (See e.g., Wellinger et al., Mol. Cell. Biol., 13:4057 [1993]). In addition, it has been observed that in humans, telomerase activity is not detectable in most somatic tissues, although it is detected in many tumors (Wellinger, supra). This telomere length may serve as a mitotic clock, which serves to limit the replication potential of cells in vivo and/or in vitro. What remains needed in the art is a method 25 to study the role of telomeres and their replication in normal as well as abnormal cells (i.e., cancerous cells). An understanding of telomerase and its function is needed in order to develop means for use of telomerase as a target for cancer therapy or anti-aging processes.
Despite the wide-ranging and expensive efforts expended in researching, developing and evaluating new treatments and cures for tumors and cancers, no truly significant advances or completely satisfactory treatments have thus far been achieved.